Next.js

[!NOTE] This release is backporting bug fixes. It does not include all pending features/changes on canary.

Core Changes

• Turbopack: Update to swc_core v50.2.3 (#87841) (#88296)
  • Fixes a crash when processing mdx files with multibyte characters. (#87713)
• Turbopack: mimalloc upgrade and enabling it on musl (#88503) (#87815) (#88426)
  • Fixes a significant performance issue on musl-based Linux distributions (e.g. Alpine in Docker) related to musl's allocator.
  • Other platforms have always used mimalloc, but we previously did not use mimalloc on musl because of compilation issues that have since been resolved.

Credits

Huge thanks to @mischnic for helping!

Core Changes

• Turbopack: more dead code: #88505
• fix(build): prevent route handler manifests from inheriting unrelated client components: #88419
• Upgrade React from 65eec428-20251218 to 3e1abcc8-20260113: #88530
• Better typesafety for interopDefault: #88486
• keep next-env.d.s unchanged between dev and build: #88428
• Remove sibling caches from CacheNode tree: #87991
• Upgrade React from 3e1abcc8-20260113 to 4a3d993e-20260114: #88547
• Finish deleting Mutable from router implementation: #88046

Misc Changes

• Remove lerna bootstrap from the clean script in package.json: #88527
• docs: add useSearchParams and useParams documentation for Pages Router: #88429
• Turbopack: Clean up VcRead::Repr associated type: #88456
• [cna] Avoid error with out-of-box Netlify config: #88546
• [turbopack] Move some of the logic for issue filtering into the rust layer: #88511
• Update Rspack production test manifest: #88469
• Update Rspack development test manifest: #88470

Credits

Huge thanks to @mischnic, @timneutkens, @unstubbable, @huozhi, @acdlite, @bgw, @karlhorky, @lukesandberg, and @vercel-release-bot for helping!

Misc Changes

• Turbopack: fix bad performance edge case in production chunking: #88508

Credits

Huge thanks to @sokra for helping!

Misc Changes

• [test] Always run all tests without aborting on failure: #88435
• Turbopack: remove sourcemapping comments: #88217
• Turbopack: use mimalloc on Linux musl: #88426
• Turbopack: add support for selective reads of keyed cell values: #88303
• Turbopack: Reduce usage of parse_quote in turbo-tasks-macros: #88454
• Turbopack: don't cell in async map: #88473
• Turbopack: replace is_reference_used with unused_references set: #88304
• Turbopack: add lint rule to not cell in async map: #88474
• Turbopack: Remove dead generic_type_macro code: #88455
• Turbopack: remove unused code: #88497
• Turbopack: improve cell order lint rule: #88498
• Turbopack: parallelize making dependent tasks dirty: #86755

Credits

Huge thanks to @unstubbable, @mischnic, @sokra, and @bgw for helping!

Core Changes

• Revert "prevent browser cache from using stale RSC responses from pre…: #88457

Credits

Huge thanks to @ztanner for helping!

Core Changes

• Don't import typescript at runtime: #88321
• fix: use RDC for server action requests: #88129
• Warn when overriding Cache-Control header on /_next/ routes: #88353
• [prebuilt-skew-protection] feat: adding in automatic deploymentId: #88012
• Revert "[prebuilt-skew-protection] feat: adding in automatic deploymentId": #88449
• Turbopack: Update reqwest, remove experimental system TLS feature: #88290

Misc Changes

• Update AGENTS.md with PR template and test generation requirements: #88417
• Add .cursor/worktrees.json configuration: #88415
• docs: add guidance for code block highlight line numbers to AGENTS.md: #88430
• [turbopack] Compute transitive side effects and use them to trim imports: #86675
• fix(turbo-tasks-backend): use correct TaskDataCategory for is_immutable check: #88331
• perf(turbo-tasks-backend): use DefaultStorage for AggregationNumber to save memory: #88336
• [Turbopack] Move DirList to its own module: #88256
• docs: add rebuild guidance and ICE troubleshooting to AGENTS.md: #88337
• Type-check run-tests.js and remove unused related flag: #88433
• [test] Remove obsolete reference to NEXT_TEST_SKIP_RETRY_MANIFEST: #88434
• Revert "[Turbopack] Move DirList to its own module": #88441
• [scripts] Avoid conflicting type for pack-next --compress: #88439
• Update Rspack production test manifest: #88403
• Update Rspack development test manifest: #88404

Credits

Huge thanks to @mischnic, @timneutkens, @lukesandberg, @ztanner, @andrewimm, @unstubbable, @eps1lon, @brookemosby, @vercel-release-bot, and @bgw for helping!

Core Changes

• Track search string as part of "refresh state": #87203
• Pass RouteTree into navigation function: #87256
• Read from segment cache unknown routes: #87293
• Pass loading boundary as part of RSC data: #87825
• Revert "refactor: consolidate PPR into cacheComponents architecture (#88243)": #88421
• fix: support TypeScript noUncheckedSideEffectImports for CSS imports: #88199

Misc Changes

• docs: fix CSP example to only include unsafe-eval in development: #88407
• docs: add PR description guidance to AGENTS.md: #88408
• ci: Fix retry comments in workflow files: #88412
• [test] Deflake test/integration/invalid-custom-routes/test/index.test.ts: #88416
• [test] Remove rogue debug log: #88423

Credits

Huge thanks to @acdlite, @timneutkens, @unstubbable, @eps1lon, @wyattjoh, and @Rani367 for helping!

Misc Changes

• Stats Action: Add ready in time: #88283
• fix: skip stats-aggregate job for docs-only changes: #88330

Credits

Huge thanks to @timneutkens for helping!

Core Changes

• refactor: consolidate PPR into cacheComponents architecture: #88243
• Turbopack: include fewer traced files for standalone: #88322
• feat(turbopack): add resolve plugin condition variant of Always and Never: #88190
• perf: use length = 0 to clear the logging array: #88244
• Time logs: Show full millisecond instead of 1 decimal: #88313
• [turbopack] Enable inferring module side effects by default: #87216

Misc Changes

• Turbopack: Use format! instead of anyhow! inside of anyhow::Context::with_context calls: #88293
• Turbopack: pull in updated vercel/nft tests: #88162
• Fix pack-next script for next-swc: #88126
• Turbopack: use correct flags in tests: #88307
• Turbopack: fix task category on reading cells: #88309
• agent.md: Explain where the Next.js core code lives: #88314
• Turbopack: improve next-server.nft.json tests: #88320
• Turbopack: add family to database read span: #88323
• Tests: Reduce loglines from apply patch delay: #88224
• Turbopack: prefetch children too: #88324
• Turbopack: more stale details for tracing: #88306
• Turbopack: make GraphTraversal deterministically calling all nodes before erroring: #88119
• Turbopack: improve error message for incompatible swc plugins: #86346
• Update Rspack development test manifest: #88301
• Update Rspack production test manifest: #88300

Credits

Huge thanks to @bgw, @wyattjoh, @mischnic, @sokra, @timneutkens, @xusd320, @huozhi, @lukesandberg, and @vercel-release-bot for helping!

Core Changes

• next/image: support custom cache handlers: #88248
• feat: add Claude Code plugin marketplace with Cache Components skill: #87993

Misc Changes

• Turbopack: remove unused code: #88274
• Turbopack: escape colon in output names: #88273
• [test] Add a failing test for cycle serialization in segment prefetches: #88287
• Turbopack: scope hoisting bug with reexport-self-star: #86131
• Turbopack: Add #[automatically_derived] to proc macros: #88281
• Update Rspack development test manifest: #88260

Credits

Huge thanks to @mischnic, @ztanner, @unstubbable, @bgw, @vercel-release-bot, and @wyattjoh for helping!

Core Changes

• Fix relative same host redirects in node middleware: #88253
• Remove loadConfig from main development process, pass value from child process: #88230
• Update deploy adapters outputs and handler interfaces for node and edge: #88247
• Move Ready in time before handler initialization: #88235

Misc Changes

• ci: fix javascript-urls test to account for React 18: #88249
• Turbopack: Remove tokio and turbo-task handles from Invalidator: #88242
• Turbopack: remove Stateful flag: #88196
• Upgrade to rustc 2026-01-04: #88095
• Turbopack: include children count in "task execution completed" span: #87318
• Turbopack: avoid blocking tasks for I/O work: #87661
• Turbopack: flatten trace when it reaches cut off depth: #88118

Credits

Huge thanks to @ztanner, @bgw, @ijjk, @sokra, @mischnic, and @timneutkens for helping!

Core Changes

• fix overlay frames cannot be opened sometimes: #88210
• Handle pnpm-workspace.yaml while searching for monorepo root: #74818
• Add more debug logs to 'use cache' wrapper: #88219
• Omit unused arguments from 'use cache' function calls: #86920
• Only log pending revalidates... debug log if applicable: #88221
• fix(next/image): bump sharp@0.34.5: #88238
• Disallow javascript urls in router methods and redirects: #88185

Misc Changes

• Turbopack: Use batch get request to read more efficient from database: #87106
• Turbopack: improve aggregation update performance: #87317
• Add test creation instructions to agents.md: #88215
• Turbopack: report changed env vars in tracing: #88195
• Turbopack: get rid of some manual self.await-s: #88236
• Guard against Object/Array shadowing in 'use cache' transform: #88229
• feat(turbo-tasks-fs): support multi denied_paths: #88186
• Upgrade to swc 54: #88207

Credits

Huge thanks to @huozhi, @sokra, @timneutkens, @unstubbable, @styfle, @mischnic, @lubieowoce, @xusd320, and @gnoff for helping!

Core Changes

• Add maximum size limit for postponed body parsing: #88175
• metadata: use fixed segment in dynamic routes with static metadata files: #88113
• feat: add --experimental-cpu-prof flag for dev, build, and start: #87946
• Add experimental option to use no-cache instead of no-store in dev: #88182

Misc Changes

• fix: move conductor.json to repo root for proper detection: #88184
• Turbopack: Update to swc_core v50.2.3: #87841
• Update generateMetadata in client component error: #88172
• ci: run stats on canary pushes for historical trend tracking: #88157
• perf: improve stats thresholds to reduce CI noise: #88158

Credits

Huge thanks to @wyattjoh, @bgw, @timneutkens, @feedthejim, and @huozhi for helping!

Core Changes

• add compilation error for taint when not enabled: #88173
• feat(next/image)!: add images.maximumResponseBody config: #88183

Misc Changes

• Update Rspack production test manifest: #88137
• Update Rspack development test manifest: #88138
• Fix compile error when running next-custom-transform tests: #83715
• chore: add Conductor configuration for parallel development: #88116
• [docs] add get_routes in mcp available tools: #88181

Credits

Huge thanks to @vercel-release-bot, @ztanner, @mischnic, @wyattjoh, @huozhi, and @styfle for helping!

Core Changes

• [strict-route-types] Typecheck App Router page props: #87386
• [strict-route-types] Enforce common React Component return types in App Router: #87389
• [strict-route-types] Switch to satisfies when validating page and route modules: #87398
• [strict-route-types] Don't reject number in config.api.bodyParser.sizeLimit when validating route: #87633
• Revert "dx: avoid next-env.d.ts change in dev": #88153
• [strict-route-types] Typecheck pages router routes in absence of App Router: #87628
• [strict-route-types] Ensure cache profiles and routes are type-checked even if .next is excluded: #87768

Misc Changes

• [turbopack] Populate the names field of sourcemaps: #87911
• Turbopack: fix order of breadth first edges: #88117
• Turbopack: transpile CHUNK_SUFFIX: #88128
• chore: add dev boot profiling and benchmark scripts: #87940
• perf: improve stats action reliability and reduce CI noise: #87945

Credits

Huge thanks to @lukesandberg, @sokra, @eps1lon, @mischnic, and @feedthejim for helping!

Core Changes

• chore: warn when running tests against stale build: #88001
• Redesign default error pages with cleaner, more user-friendly UI: #87988
• dx: avoid next-env.d.ts change in dev: #88103
• prevent browser cache from using stale RSC responses from previous builds: #86554

Misc Changes

• chore: add Claude Code configuration: #87943
• test: reduce flakiness in opentelemetry test for prod mode: #88102
• Rename CLAUDE.md to AGENTS.md with symlink: #88105

Credits

Huge thanks to @feedthejim, @huozhi, and @ztanner for helping!

Core Changes

• fix: revalidateTag with profile should not trigger client cache invalidation: #88069

Credits

Huge thanks to @feedthejim for helping!

Misc Changes

• fix: normalize CRLF line endings in jscodeshift tests on Windows: #88008

Credits

Huge thanks to @feedthejim for helping!

Misc Changes

• chore(turbo-tasks-malloc): replace mimalloc-rspack to mimalloc: #87815

Credits

Huge thanks to @xusd320 for helping!

Core Changes

• misc: fix type check log for CI envs: #87838

Misc Changes

• Update Rspack production test manifest: #87889
• Update Rspack development test manifest: #87888

Credits

Huge thanks to @feedthejim and @vercel-release-bot for helping!